BURLEY, Idaho - Flood irrigation practices in the early days of irrigation on the Eastern Snake River Plain boosted water levels in the aquifer, which lay beneath it. But as irrigation efficiencies improved, less water reached the aquifer, contributing to its decline.
One issue now is in trying to get more water to the aquifer by recharging it.
The state of Idaho and irrigation and canal companies have been attempting to "balance the budget" of water going in and water coming out, but it's a complicated endeavor, said Mike McVay, technical hydrologist with Idaho Department of Water Resources.
Managed recharge of the aquifer does offer a way to balance the budget, but it depends on where you recharge, he said during the Idaho Irrigation Equipment Association's conference in Burley on Wednesday.
Water injected for recharge doesn't stay in the aquifer and instead goes back to the Snake River fairly quickly, making balancing the budget a continuous effort, he said.
To assist in analysis of recharge, McVay has modeled the results of recharge efforts from 2007 to 2011.
During that time, irrigation and canal companies on the Eastern Snake River Plain participated in recharge efforts at several locations, sending 100,000 acre-feet per year into the aquifer.
But "the aquifer is not a very good bathtub, it leaks a lot," he said. Water tends to go back to the river.
That's not necessarily bad. It depends on water-management goals, with different benefits at different sites. In addition to raising aquifer-storage levels, those goals could be increasing flows in the river, springs and reservoirs, McVay said.
The goal of the state is to keep water in the aquifer for people to use, but it's a complicated issue. The state has to balance obligations for the Swan Falls Agreement-which balances water uses for agriculture and water needs for hydropower generation-and river and spring flows to keep water rights whole, he said.
McVay's models help evaluate recharge efforts by analyzing where the water is going.
In the theoretical modeling, McVay kept pumping water into the model, much more than the recharge sites can take, to see where the water would go. In both the theoretical and actual modeling, the impact on the aquifer was small.
If it isn't continuously recharged, the water will leak into the river, no matter how much is put in. That's because the aquifer is like a big bowl with a hole in the bottom, he said.
In addition, the theoretical modeling doesn't take into account other factors, such as weather or physical limitations, he said.
It is a tool that shows how the aquifer behaves. But the bottom line is the aquifer leaks and sooner or later, water is going to go back to the river, McVay said.
The take-home message is the aquifer has to continually be recharged or it will all leak out, he said.